This invention relates to an apparatus for dynamically balancing rotating objects while they are in motion and a method for making the inventive apparatus. The inventive apparatus can be used to balance wheels of vehicles or shafts of rotating machinery. A mounting fixture that supports counterbalancing weights is attached to a rotating object. The weights in the apparatus are free to move relative to the rotating object in an orbit concentric to the axis of rotation of said rotating object. Under the influence of the forces generated by rotation of the rotating object above its critical speed, the weights take a configuration that oppose and partially cancel the imbalance of the rotating object; this results in less undesired vibration.
Dynamic balancing of rotating objects is known in the prior art. Reference is made to the following patents and publications: U.S. Pat. Nos. 3,164,413 to Salathiel, 3,316,021 to Salathiel, 3,346,303 to Wesley, 3,376,075 to Mitchell, 3,733,923 to Goodrich, 3,799,619 to LaBarber, 3,913,980 to Cobb, 3,953,074 to Cox, and 4,674,356 Kilgore describe inventions used to dynamically balance rotating objects, usually vehicle wheels.
U.S. Pat. Nos. 3,164,413 and 3,316,021 to Salathiel describe a hollow annular hoop containing a plurality of the spherical weights and a damping fluid. In use, the hoop is attached to a rotating wheel perpendicular to the axis of rotation of the wheel and concentric to the axis of rotation. The weights are free to move within the hoop. The damping fluid reduces noise as well as restricts the free movement of the weights. The weights are urged toward the point in the hoop which offsets the imbalance of the wheel. The annular hoop is made of a plastic material. The apparatus in the Salathiel patents has the disadvantage of using a deformable material for the annular hoop. Under conditions of rotation at high speed, the hoop can bulge where it is free to move. This loss of concentricity causes an imbalance to the device. Loss of concentricity of the hoop can also prevent free movement of the weights.
U.S. Pat. No. 3,346,303 to Wesley describes a hollow annular hoop containing a plurality of spherical weights and a measured amount of damping fluid. Wesley provides a hoop with an apex at the outer perimeter of the hoop. The hoop is adapted with the outer apex to provide reduced areas of contact between the spherical weights used and the hoop when the hoop is rotated. A damping fluid is also used in the Wesley patent. The hoop is constructed of a metal formed or welded into the proper shape or configuration. The hoop is attached to the wheel of a vehicle by use of the existing lug nuts on the wheel. The hoop is attached to a mounting fixture which has several precut lug nut holes adapted to fit a wheel.
U.S. Pat. No. 3,376,075 to Mitchell describes a dynamic wheel balancer which has a hollow annular hoop with a plurality of spherical weights and a damping fluid. The hoop is attached to a mounting fixture which is adapted to fit a variety of wheel and lug nut configurations. The annular hoop is constructed by attaching a U-shaped channel onto a plate in a fluid tight manner.
U.S. Pat. No. 3,733,923 to Goodrich describes a balancer for rotating masses which uses an annular hoop, spherical weights and a damping fluid. The hoop is a continuous metallic chase containing carbon steel balls in a damping fluid. The hoop contains a small section on the interior portion which is removed for adding the weights and the fluid.
U.S. Pat. No. 3,799,619 to LaBarber describes a vibration dampening assembly which comprises an annular hoop and spherical weights within the hoop. The outer perimeter of the hoop wall has deformable material placed thereon to assist in retaining the spherical weights in position after they have been distributed by the rotating of the hoop.
U.S. Pat. No. 3,913,980 to Cobb for a dynamic wheel balancing apparatus discloses a annular hoop with spherical weights which is placed around a wheel inside a tire of a vehicle. The invention uses non-metallic weights and a damping fluid. The hoop is made of an elastic material which can deform in use at high rotational speeds.
U.S. Pat. No. 3,953,074 to Cox discloses an annular hoop made of an aluminum outer hoop and short segments of flexible tubing placed inside the outer hoop. A plurality of spherical weights are set inside the hoops. The segments of flexible tubing are allowed to move within the outer hoop during rotation of the device. The weights are sized to move freely inside the inner bore of the flexible tubing. Both the weights and the flexible tubing are free to move with the rotation of the device, thus balancing an imbalanced wheel.
U.S. Pat. No. 4,674,356 to Kilgore describes a dynamic rotational Counterbalance Structure adapted to rotating object. A cylindrical body with an outer groove is disclosed. The outer groove is sized to accept a plurality of spherical weights. A band is fitted around the groove. A Damping fluid is also introduced into the enclosed channel with the weights. In use, the device is fitted to a rotating object where the damped weights offset imbalances in the rotating object.
The publication DESIGN NEWS described the concept of "Self-Compensating Balancing in Rotating Mechanisms", in an article dated Apr. 28, 1965. Four requirements for successful application of the method for self compensating balancing are described. First, there must be inertial forces on the rotating shaft that cause the mass center to misalign with the rotation center of the support bearings. Second, the rotating part must operate above its critical speed (i.e., the speed at which the shaft resonants and deflections are maximum). Third, the bearings must have resiliency. Fourth, the rotor must be sufficiently balanced to avoid damage to itself as it passes through critical speed during startup. An intuitive description of the underlying phenomena is also given.
The prior art does not provide a practical and effective apparatus for realizing the benefits of dynamical balancing for many possible applications. The art fails to provide a design with the required precision and durability at a cost commensurate with the benefits.